Transcript Slide 1

Carbohydrates in Exercise and Recovery
Advanced Level
Module I
Carbohydrates: Definitions, Digestion, and Absorption
Review of Carbohydrate Metabolism
Carbohydrates: Glycogen Storage
Carbohydrates:
Definitions, Digestion, and Absorption
Importance of Carbohydrates in Sports Nutrition
 Carbohydrates are a major fuel source for exercising muscle,
especially as exercise intensity and duration increase
 Types of carbohydrate oxidation
– Exogenous: Oxidizing carbohydrates ingested from the diet
– Endogenous: Breaking down stored carbohydrate (ie, glycogen)
for energy needs
 Carbohydrates can also influence fluid absorption from the
intestine (hydration)
 Some carbohydrates can cause gastrointestinal intolerance and
could impair performance for that reason
United States Anti-doping Agency. Optimal dietary intake guide. Available at:
http://www.usada.org/diet/?gclid=COOM-Ky95aYCFQTNKgodzVQL2w. Accessed January 31, 2011.
4
Carbohydrate Digestion and Absorption
 Carbohydrates are found in the diet as
– Free monosaccharide (1 sugar unit) or
– Larger saccharides (chains of monosaccharides)
 Enzymes must digest larger saccharides down to individual
monosaccharides before these monosaccharides can be absorbed
– Carbohydrates that escape absorption make their way to the colon
(variable degrees of bacterial fermentation)
 Monosaccharides are absorbed from the intestine mainly via
active transport (energy-requiring) or facilitated diffusion
– Both active transport and facilitated diffusion require transporters
• SGLT (Active transport)
• GLUT (Facilitated diffusion)
Abbreviations: SGLT, sodium-glucose linked transporter; GLUT, glucose transporter.
Holmes R. J Clin Pathol. 1971;S3-5:10-13. doi:10.1136/jcp.s3-5.1.10.
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Why Do We Need to Know About Carbohydrate
Absorption in Sports Nutrition?
 The ability of the intestine to absorb a carbohydrate can
be the rate-limiting step for its delivery to muscle cells
for fuel use
– Intestinal sugar transporters can become saturated, resulting in
malabsorption of a carbohydrate
 Concept of multiple transportable carbohydrates
– Use a blend of sugars that require different transporter systems
– May increase carbohydrate absorption relative to using just a
single sugar
 Enzyme systems in the intestine may be insufficient to
digest some carbohydrates (eg, lactose intolerance)
6
Sugar Transport in an Intestinal Epithelial Cell
Intestinal Lumen
Glucose
Galactose
Enterocyte
Glucose
Galactose
SGLT1
2 Na+
Blood
Glucose
Galactose
Fructose
Glucose
Galactose
Fructose
GLUT2
2 Na+
Na+
Na+
ATP
Fructose
Fructose
GLUT5
Apical membrane
ADP + Pi
K+
K+
Basolateral membrane
Abbreviations: ADP, adenosine diphosphate; ATP, adenosine triphosphate; GLUT, glucose transporter; K, potassium; Na, sodium; Pi, phosphate group;
SGLT, sodium-glucose linked transporter.
Scheepers A, et al. JPEN J of Parenter Enteral Nutr. 2004;28(5):364-371.
Drozdowski LA, et al. World J Gastroenterol. 2006;12(11):1657-1670.
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Major Dietary Monosaccharides
No Digestion Required for Absorption
 Glucose; from corn and other plants
– Also called dextrose
– Absorbed primarily by active transport (SGLT1), with facilitated diffusion (GLUT2)
used to a lesser extent when intraluminal glucose concentrations are high
• SGLT1 requires sodium co-transport and ATP
– Transported out of enterocyte via GLUT2
– Muscles express GLUT4 transporters to take up glucose from the blood
 Fructose; fruit sugar
–
–
–
–
Absorbed by facilitated diffusion (primarily GLUT5)
Simultaneous presence of glucose stimulates fructose uptake, probably by GLUT2
Transported out of enterocyte via GLUT2
Fructose is taken up almost entirely by the liver; very little circulates in the blood
 Galactose
– Is a component of lactose (milk sugar)
– Is transported from the intestine similarly to glucose
– Converted to glucose in the liver
Abbreviations: ATP, adenosine triphosphate; SGLT, sodium-glucose linked transporter; GLUT, glucose transporter.
McGrane MM. Carbohydrate metabolism—synthesis and oxidation. In: Stipanuk M. Biochemical, Physiological & Molecular Aspects of Human Nutrition. 2nd
Edition. Saunders/Elsevier; 2006: chap 12.
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Common Dietary Disaccharides
 Sucrose (table sugar)
– Extracted from sugar cane and beets
– Composed of glucose and fructose (alpha-1,2 linked)
– Digested by sucrase-isomaltase complex
• Anchored in brush border of small intestine
 Lactose
– Primary sugar in virtually all mammalian milks
– Composed of glucose and galactose (beta-1,4 linked)
– Digested by brush border lactase-phlorizin hydrolase
Hertzler SR, et al. Intestinal disaccharidase depletions. In: Shils ME, et al. Modern Nutrition in Health and Disease. 10th Edition. Baltimore, MD: Lippincott Williams
& Wilkins; 2006: pp 1189-1200.
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Common Dietary Disaccharides (continued)
 Maltose
– Found in some fermented beverages (eg, beer) and is also an
intermediate product in starch digestion
– Composed of 2 glucose molecules (alpha-1,4 linked)
– Digested by maltase-glucoamylase
 Trehalose
– Found in mushrooms
– Composed of 2 glucose molecules (alpha-1,1 linked)
– Digested by trehalase
Hertzler SR, et al. Intestinal disaccharidase depletions. In: Shils ME, et al. Modern Nutrition in Health and Disease. 10th Edition. Baltimore, MD: Lippincott Williams
& Wilkins; 2006: pp 1189-1200.
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Oligosaccharides (3-10 Monosaccharide Units)
 Oligosaccharides are found in human milk and in a
variety of fruits and vegetables
 Many of these are not digestible by human enzymes
 Examples
– Stachyose (galactose-glucose-fructose)
– Raffinose (galactose-galactose-glucose-fructose)
– Fructooligosaccharides and oligofructose
• Chains of fructose units sometimes terminated with glucose
 Glucose polymers/maltodextrins
– Most are rapidly digestible; some are resistant to digestion
Carbohydrates. In: Gropper SS, et al. Advanced Nutrition and Human Metabolism. 4th Edition. Belmont, CA: Wadsworth, Cengage Learning.; 2005: pp 63-106.
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Digestible Polysaccharides
 Plant starches (digestion via salivary and
pancreatic amylases)
– Amylopectin
• Chains of alpha-1,4 linked glucose with alpha-1,6 branch points
(renders the starch more digestible)
– Amylose
• Straight chains of glucose linked by alpha-1,4 bonds
• Less digestible than amylopectin
 Animal starch
– Glycogen
• Storage form of glucose in liver and muscles
• Similar in structure to amylopectin, but more highly branched
Carbohydrates. In: Gropper SS, et al. Advanced Nutrition and Human Metabolism. 4th Edition. Belmont, CA: Wadsworth, Cengage Learning.; 2005: pp 63-106.
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Nondigestible Polysaccharides (Dietary Fibers)
 Cellulose
– Chain of glucose units linked by beta-1,4 bonds
 Hemicelluloses
 Pectins
 Gums
 Mucilages
 Some indigestible oligosaccharides would count as
dietary fibers
Carbohydrates. In: Gropper SS, et al. Advanced Nutrition and Human Metabolism. 4th Edition. Belmont, CA: Wadsworth, Cengage Learning.; 2005: pp 63-106.
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What Is High-Fructose Corn Syrup?
 Cornstarch converted to a syrup that is essentially 100% dextrose (glucose)
 Enzymes isomerize dextrose to produce 42% fructose syrup (HFCS-42)
 Refiners draw HFCS-42 through an ion exchange column that retains fructose
– Result is HFCS-90 syrup
 The HFCS-90 syrup is blended with HFCS-42
– Result is HFCS-55
 The HFCS-55 syrup is the type used mainly in beverage industry
– Syrup is 55% fructose, 45% dextrose
– Essentially no different than sucrose (table sugar; 50% fructose, 50% glucose)
– The term “high-fructose corn syrup” is a little misleading
• Because corn syrup is 100% glucose, any presence of fructose typically results in it being
labeled “high-fructose corn syrup”
Soenen S, et al. Am J Clin Nutr. 2007;86(6):1586-1594.
Smith JS, et al. Food Processing: Principles and Applications. Ames, IA: Blackwell Publishing; 2004, p 212-214.
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What Is the Potential Concern Regarding
High-Fructose Corn Syrup?
 Animal and human studies using large amounts of fructose
(generally > 17% of total energy), relative to the same amount of
glucose, show
– Increases in blood triglyceride levels
– Decreased insulin sensitivity
– Possible increases in visceral adiposity
 Potential explanations
– Unregulated metabolism of fructose increases de novo lipogenesis
– Fructose, unlike glucose, does not generate an insulin response
• Insulin may directly lower food intake
• Insulin may increase leptin release from adipose tissue (leptin decreases food
intake)
Bantle JP, et al. Am J Clin Nutr. 2000;72(5):1128-1134.
Stanhope KL, et al. J Clin Invest. 2009;119(5):1322-1334.
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Keys to Making Sense of Fructose or
High-Fructose Corn Syrup Literature
 Pure fructose versus high-fructose corn syrup is an important issue
– Human studies have generally used pure fructose, not high-fructose corn
syrup or sucrose
 In preclinical studies, rodents have much greater ability for de novo
lipogenesis from carbohydrates than do humans
 In human studies, the level of fructose ingestion was at least
double the current national average intake
 Sex differences
– Men are more susceptible than women to the effects of fructose in blood
lipids (ie, triglycerides)
DiMeglio DP, et al. Int J Obesity. 2000;24:794-800; Melanson KJ, et al. Nutrition. 2007;23(2):103-112; Stanhope KL, et al. Am J Clin Nutr. 2008;87(5):11941203; Soenen S, et al. Am J Clin Nutr. 2007;86(6):1586-1594.
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The Truth About High-Fructose Corn Syrup
 Too much sugar, of any kind, in beverages is not recommended
– Poor compensation for carbohydrate energy consumed in beverages can
lead to weight gain
 However, there are no differences in metabolic responses to
high-fructose corn syrup and sucrose in humans
– No differences in circulating hormones
– No differences in appetite or satiety-related variables
DiMeglio DP, et al. Int J Obesity. 2000;24:794-800; Melanson KJ, et al. Nutrition. 2007;23(2):103-112; Stanhope KL, et al. Am J Clin Nutr. 2008;87(5):11941203; Soenen S, et al. Am J Clin Nutr. 2007;86(6):1586-1594.
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Review of Carbohydrate Metabolism
The Glycolysis Pathway
Glucose (6 C)
Glucokinase (liver)
Hexokinase (muscle)a
ATP
ADP
Glycogen
Glucose-6-phosphate
Cytosol
Fructose-6-phosphate
Phosphofructokinase
ATP
ADP
Fructose-1,6-bisphosphate (6 C)
Glyceraldehyde-3-phosphate (3C)
Pi
NAD
NAD + H+
1,3-bisphosphoglycerate
Dihydroxyacetone
Phosphate (3C)
Glyceraldehyde-3-phosphate
Pi
NAD
NAD + H+
1,3-bisphosphoglycerate
ADP
ATP
ADP
ATP
3-phosphoglycerate
3-phosphoglycerate
2-phosphoglycerate
2-phosphoglycerate
H20
Phosphoenolpyruvate (PEP)
Pyruvate
kinase
ADP
ATP
Pyruvate (3 C)
H20
Phosphoenolpyruvate (PEP)
Pyruvate
kinase
ADP
ATP
Pyruvate (3 C)
a
For clarity, only selected enzymes are shown.
Abbreviations: ADP, adenosine di phosphate; ATP, adenosine triphosphate; C, carbon; NAD, nicotinamide adenine dinucleotide; P i, phosphate group.
Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.
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Galactose and Glycolysis
 Galactose (Gal)
– Phosphorylated to galactose-1-phosphate (Gal-1-P) by galactokinase
– Gal-1-P converted to glucose-1-phosphate (Glc-1-P)
• Gal-1-P uridyl transferase
• Uridine diphosphogalactose 4-epimerase
– Glc-1-P then enters glycolysis as does glucose derived from glycogen
 Inborn errors of metabolism
– Can have inborn defects of the 3 enzymes of Gal metabolism (galactosemia)
– Results in accumulation of Gal in tissues such as lens of eye and damage
(cataracts) due to osmotic effect
– Gal-free diet required
 Effect of ethanol
– Inhibits the epimerase enzyme
Abbreviation: Glc, glucose.
Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.
Badawy AA-B. Alcohol and Alcoholism. 1977;12(3):120-136.
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Fructose and Glycolysis
 Fructose
– Most is taken up by the liver and phosphorylated to fructose 1-phosphate
(F-1-P) by fructokinase
– Aldolase B (liver form) splits F-1-P into glyceraldehyde and DHAP
• Both can become glyceraldehyde-3-P (part of glycolytic pathway)
• Important that this enters glycolysis past PFK regulatory step
 Inborn errors of metabolism
– Fructokinase defect (fructosuria)
• Not serious
– Aldolase B defect
• Accumulation of F-1-P
• Depletion of cellular phosphate stores
• Blocking of glycogen breakdown and gluconeogenesis
• Fructose-free diet required
Abbreviations: DHAP, dihydroxyacetone phosphate; PFK, phosphofructokinase.
Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.
Steinmann B, et al. Disorders of fructose metabolism. In: Scriver CR, Beaudet AL, Sly WS, Eds. The Metabolic and Molecular Bases of Inherited Disease. 8th ed.
New York; McGraw Hill; 2001, p 1489-1520.
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Entry of Glucose, Galactose, and Fructose Into
Liver Glycolysis
Galactose
ATP
Galactokinase
ADP
Galactose-1-phosphate
Glucose
ATP ADP
UDP-glucose:
Galactose-1-phosphate
uridyl transferase
Glucose-1-phosphate
Fructose
UDP-glucose
UDP-galactose
UDP-glucose-4-epimerase
Glucose-6-phosphate
Fructokinase
Fructose-6-phosphate
Fructose-1-phosphate
Aldolase
Phosphofructokinase
Fructose-1,6-bisphosphate
ATP ADP
Glyceraldehyde
+
Dihydroxyacetone phosphate
Glyceraldehyde-3-phosphate
+
Dihydroxyacetone phosphate
Abbreviations: ADP, adenosine diphosphate; ATP, adenosine triphosphate; UDP, uridine diphosphate.
Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.
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Pentose Phosphate Pathway, or
Hexose Monophosphate Shunt
 Alternative liver pathway for utilizing glucose
 Can be used to generate ribose for nucleotide and ATP synthesis
 Can also serve as a source of NADPH for oxidation-reduction
(redox) reactions
– Example: reduction of glutathione to maintain stability of RBC membrane
Abbreviations: ATP, adenosine triphosphate; NADPH, nicotinamide adenine dinucleotide phosphate; RBC, red blood cell.
Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.
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Gluconeogenesis
 Almost a reversal of glycolysis, but must overcome
thermodynamic barriers for 3 reactions:
– Glucokinase/hexokinase
– Phosphofructokinase
– Pyruvate kinase
 Methods of circumvention:
– Glucose-6-phosphatase
– Fructose 1,6-bisphosphatase
– Pyruvate carboxylase and phosphoenolpyruvate carboxykinase (PEPCK)
• Pyruvate carboxylase requires biotin as coenzyme
Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.
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Gluconeogenesis in Liver
Glucose
Reactions different than glycolysis
Pi
Glucose-6-phosphatase
Glucose-6-phosphate
Fructose-6-phosphate
Pi
Fructose-1,6-bisphosphatase
Fructose-1,6-bisphosphate
Dihydroxyacetone-phosphate
Glycerol
Glycerol-3-phosphate
Glycerol-3-phosphate
Phosphoenolpyruvate (PEP)
Phosphoenolpyruvate
carboxykinase (PEPCK)
TCA cycle
Amino
acids
Amino acids
oxaloacetate
Alanine
Pyruvate
carboxylase
Pyruvate
Lactate
Abbreviations: TCA, tricarboxylic acid; Pi, phosphate group.
Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.
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The Cori (Lactate) and Glucose-Alanine Cycles
Blood
Liver
Muscle
Glucose
Glucose-6-phosphate
Glycogen
Glycogen
Glucose-6-phosphate
Urea
Pyruvate
Lactate
Lactate
Lactate
Pyruvate
NH2
Pyruvate
NH2
Alanine
Alanine
(eg, from leucine)
Alanine
Abbreviation: NH2, amino functional group.
Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.
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Glycogen
 Glycogen is degraded by a different pathway than its synthesis
– Key enzyme for degradation is the activation of glycogen phosphorylase
 Vitamin B6 (pyridoxal phosphate) is a structural part of glycogen
phosphorylase
 Several types of glycogen storage disorders
– Deficiencies of
• Glucose-6-phosphatase
• Lysosomal alpha 1  4 and 1  6 glucosidase (acid maltase)
• Debranching enzyme
• Muscle phosphorylase
• Liver phosphorylase
• Others
Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.
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Glycogenesis/Glycogenolysis in Liver
and Muscle
Branching
enzyme
-1,4 glucose units
UDP
Glycogen
(-1,4 and -1,6
glucose units)
Glycogen
phosphorylase
Glycogen
synthase
Pi
Glycogen primer + UDP-glucose
Glucan transferase/
debranching enzyme
PPi
UDP
ATP
Glucose-1-phosphate
ADP
Glucose-6-phosphate
Glucose-6-phosphatase
(liver only)
Free glucose
Glucokinase (liver)
Hexokinase (muscle)
Glucose
Abbreviations: ADP, adenosine diphosphate; ATP, adenosine triphosphate; P i, phosphate group; PPi, pyrophosphate; UDP, uridine diphosphate.
Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.
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Carbohydrates: Glycogen Storage
Storage of Carbohydrate in the Body
 Glucose that is absorbed, but not immediately needed, is stored
as glycogen
–
–
–
–
Found in the liver and skeletal muscles
It is similar to starch
Glycogen in liver is a reserve glucose supply to the brain
Glycogen in muscles is an energy source for exercise
 Glycogen synthase in muscles is at peak activity immediately
following glycogen-depleting exercise
– Eat carbohydrates immediately after exercise for most rapid glycogen
replenishment
United States Anti-doping Agency. Optimal dietary intake guide. Available at: http://www.usada.org/diet/?gclid=COOM-Ky95aYCFQTNKgodzVQL2w.
Accessed January 31, 2011.
Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman and Co.; 2002.
30
Glycogen Distribution in the Body
 Liver
– 60 to 120 g (4% to 8% of liver weight, overnight fasting versus fed,
respectively)
– Liver glycogen is generally quite depleted by overnight fasting
 Skeletal muscle
– 200 to 500 g (highly variable)
 Effects of training and carbohydrate loading on muscle glycogen
stores
– Untrained, normal diet
– Trained, normal diet
– Trained, carbohydrate-loaded
80 to 90 mmol/kg muscle (wet weight)
130 to 135 mmol/kg muscle (wet weight)
210 to 230 mmol/kg muscle (wet weight)
Coleman E. Today’s Dietitian. March 2002:15-18.
Flatt JP. Am J Clin Nutr. 1995;61(suppl):952S-959S.
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Glycogen Terminology
 Terms related to glycogen synthesis
– Glycogen synthase (enzyme that forms glycogen)
– Glycogenin (primer for glycogen synthesis)
– Proglycogen
• Initial phase of glycogen synthesis (glycogenin + small number
of glucose molecules)
– Macroglycogen
• Larger ratio of glucose molecules to glycogenin
• Forms to a greater extent vs proglycogen after 2 to 3 days of
high-carbohydrate diet
 Terms related to glycogen breakdown
– Glycogen phosphorylase
• Breaks down glycogen, with ultimate formation of glucose-6-phosphate
– Glucose-6-phosphatase
• Necessary to release the glucose from cell into blood
• Enzyme is present in liver, absent in skeletal muscle
– Muscle glycogen for local use only
Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman and Co.; 2002.
Huang M, et al. J Clin Invest. 1997;99(3):501–505. doi:10.1172/JCI119185.
32
Muscle Glycogen, g/100 g tissue
Muscle Glycogen Storage—Effects of Exercise
KS
PT
RB
RG
DC
Average
(N = 4)
2.5
2.0
1.5
1.0
0.5
PRE
POST
PRE
POST
PRE
POST
10 miles
10 miles
10 miles
Day 1
Day 2
Day 3
5TH DAY
POST
Diet: carbohydrate, 40% to 50% kcals; fat, 30% to 40% kcals; protein, 10% to 15% kcals.
Costill DL, et al. J Appl Physiol. 1971;31(6):834-838.
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Factors Influencing Muscle Glycogen Synthesis
 Energy and CHO availability
 Timing of meals relative to completion of exercise
(sooner the better)
 Additional protein possibly
 GI of CHO (higher GI = faster)
 Degree to which glycogen is depleted (more depletion = faster)
 Rest (tapering of exercise is necessary)
 Sex
– Men and women respond equally (ie, glycogen storage) if energy and CHO
are adequate
– Women seem to be less reliant on CHO and more reliant on fat during
exercise than men
Abbreviations: CHO, carbohydrate; GI, glycemic index.
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Muscle Glycogen Storage—
Effects of Diets With Differing CHO Levels
 Simple and complex CHO had equal glycogen resynthesis within the first
24 hours postexercise
Change in Muscle Glycogen
(mmol/kg muscle/24 hr)
– Complex CHO had somewhat greater glycogen synthesis during subsequent 24 hours
80
a
70
60
± SE
50
40
30
20
10
7
meals
2
meals
0
25%
50%
70%
70%
CHO diets, % of calories
 Runners performed glycogen-depleting exercise before dietary intake
 Diets differed in percent of kcals from CHO, CHO type, and number of meals
Abbreviations: CHO, carbohydrate; SE, standard error.
a Significant difference between the mean and the mean change in muscle glycogen observed during the mixed diet (50% of cal from CHO).
Reprinted from Costill DL, et al. Am J Clin Nutr. 1981;34(9):1831-1836.
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Can Protein Boost the Rate of
Glycogen Storage?
 Mixed results in clinical studies
– Yes
• Zawadski KM, et al. J Appl Physiol. 1992;72:1854-1859
• Ivy JL, et al. J Appl Physiol. 2002;93:1337-1344
– No
• Roy BD, et al. J Appl Physiol. 1997;83:1877-1883
• Jentjens RL, et al. J Appl Physiol. 2001;91:839-846.
• Van Hall G, et al. J Appl Physiol. 2000;88:1631-1636.
 Key issues
– More frequent feeding intervals did not show benefit with protein
– Adequacy of carbohydrate and protein intake
• Protein may be more important if athlete is unable to consume enough
carbohydrate
36
Effect of Carbohydrate and Protein on
Muscle Glycogen During Recovery
Muscle Glycogen Storage Rate,
µmol/g pro/hour
40
a,b
112 g CHO, 41 g protein
112 g CHO
41 g protein
30
a
20
10
0
CHO-PRO
CHO
PRO
 Subjects ingested diet immediately and 2 hours after glycogen-depleting
exercise; glycogen storage was assessed immediately and 4 hours postexercise
a
Significantly faster compared with PRO (P < .05).
faster compared with CHO (P < .05).
Abbreviations: CHO, carbohydrate; Pro, protein.
Zawadzki KM, et al. J Appl Physiol. 1992:72(5):1854-1859.
b Significantly
•
37
Muscle Glycogen Storage, mmol/L
Effects of Carbohydrate-Protein Combination
on Muscle Glycogen Storage During Recovery
120-240 min
60
a
40-120 min
50
0-40 min
40
CHO-Pro:
80 g CHO, 28 g protein, 6 g fat
HCHO:
108 g CHO, 6 g fat
LCHO:
80 g CHO, 6 g fat
30
20
10
0
CHO-PRO
HCHO
LCHO
 Subjects ingested diet immediately and 2 hours after glycogen-depleting
exercise; glycogen storage was assessed immediately, at 20 and 40 minutes,
and at 1, 2, 3, and 4 hours postexercise
a
Significantly higher compared with HCHO (P = .013) and LCHO (P = .004).
Abbreviations: CHO, carbohydrate; Pro, protein; HCHO, high carbohydrate; LCHO, low carbohydrate.
Reprinted from Ivy JL, et al. J Appl Physiol. 2002;93(4):1337-1344.
38
Muscle Glycogen Resynthesis With Different
Diets After Exercise
 A diet of fat plus protein following exercise was not able to restore
pre-exercise levels of muscle glycogen up to 4 days later
− However, a carbohydrate diet restored muscle glycogen within 2 days
Day 1
Day 2
Day 3
Day 4
Day 5
9 AM
Immediate
5 PM
9 AM
9 AM
9 AM
9 AM
Diet
Fasting
F+P
F+P
F+P
F+P
MG
1.66
0.01
0.36
0.43
0.63
0.76
0.70
Diet
Fasting
F+P
F+P
F+P
F+P
MG
1.24
0.01
0.20
0.22
0.24
0.47
0.91
PRE-EXE
POST-EXE
POST-EXE
Day 6
5 PM
Day 7
Day 8
Day 9
9 AM
9 AM
9 AM
5 PM
Subject 1
F+P
CHO
1.02
0.61
1.61
Subject 2
F+P
F+P
CHO
1.10
2.11
Abbreviations: Exe, exercise; MG, muscle glycogen (g/100 g wet muscle tissue); F+P, 2000 kcal from fat and protein (<5% carbohydrate); CHO, 2000 kcal from
carbohydrate ( 95% carbohydrate).
Hultman E and Bergström J. Acta Med Scand. 1967;182(1):109-117.
39
Timing of Postexercise Carbohydrate Ingestion
and Glycogen Resynthesis
 Maximal glycogen synthase is within 2 hours of exercise
– “Window of opportunity” to promote faster glycogen repletion
 Glycogen synthesis at 2 hours postexercise: more rapid with
carbohydrate ingestion immediately postexercise vs carbohydrate
ingestion delayed 2 hours postexercise
– However, the delayed ingestion group can catch up within 24 hours given
adequate carbohydrate intake
 Key advantage of carbohydrate ingestion immediately postexercise
is for athletes with multiple events in a short time span
– Need fast glycogen recovery
Ivy JL, et al. J Appl Physiol. 1988;64(4):1480-1485.
Parkin JA, et al. Med Sci Sports Exerc. 1997;29(2):220-224.
Burke LM, et al. J Sports Sci. 2004;22:15-30.
40
Timing of Postexercise Carbohydrate Ingestion
and Glycogen Resynthesis (continued)
2
4
P < .05
P < .05
20
40
Muscle Glycogen Storage,
mmol/kg wet weight1
Time Postexercise, hours
Time Postexercise, hours
Immediate feeding
Delayed feeding (2 hours)
8
NS
24
NS
50
100
Muscle Glycogen Storage,
mmol/kg wet weight2
1. Ivy JL, et al. J Appl Physiol. 1988;64(4):1480-1485.
2. Parkin JA, et al. Med Sci Sports Exerc. 1997;29(2):220-224.
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Summary of Key Messages
 Carbohydrates are the major energy source for exercising muscle
 The type of carbohydrate consumed influences the availability of
energy to the muscle
– Absorption and digestion are key steps
 Excess carbohydrates in the body can be stored as glycogen for
later muscle use
– A high-carbohydrate diet helps to maximize glycogen stores and generally
increases exercise performance
– Postexercise meal content and timing can optimize glycogen resynthesis
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